Disc brake problem

Suspension, Brakes, Tires, Wheels etc..

Disc brake problem

Postby bigblockdodge440 » Fri Apr 28, 2017 6:11 pm

Hi! Been a while since I was on. Don't get to get on very much. Anyway I have a couple of problems. I put disc brakes on my son's 71 SWEPTLINE D100 from SCAREBIRD, I did not put a proportioning valve on it, my problem is it does not start to stop until around 3 to 4 inches from the floor and goes just about to the floor when I make a hard stop. I bench bled the master cylinder, gravity bled the brakes all the way around, and then had my son mash the brake pedal and bled them that way. I also would like to know if I should use the distribution block off of my 84 dodge ram charger. I have been working on cars for my self about forty years and have never ran across this problem. Please help this is his every day driver. Thanks for any info.
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Re: Disc brake problem

Postby Txas2step » Fri Apr 28, 2017 6:50 pm

This is what i used on my '61 and '67 swepts with the scarebird. :Thumbsup
http://www.ebay.com/itm/Brake-Combinati ... 4d07d4c59f
61 shorty 170/ 3spd 3:91(sold)
66 lwb 318 poly/727/4:10 (sold)
67 shorty 318poly/4spd 3:55
68 ute 318/3 spd/3:55(sold)
70 318/727/3:23
66 d200 225/4spd/4:10( military)(sold)
68 d100 383/727/3:55
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Re: Disc brake problem

Postby bigblockdodge440 » Sat Apr 29, 2017 7:03 am

Thanks Txas2step I will try that if my ram charger one don't work. Have to save money any way I can, and thanks again.
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Re: Disc brake problem

Postby Conrad » Sat Apr 29, 2017 7:48 pm

Thanks for that link. The 'residual pressure valves' will help from what I have read.
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Re: Disc brake problem

Postby Crewcabstripper » Sun Apr 30, 2017 9:43 pm

I'm interested in seeing if the ram charger proportioning valve will work. I'm going to be doing the scarebird swap on my d200 as soon as my brackets get here. Was thinking of using the disc/drum valve from my 78 f250
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Re: Disc brake problem

Postby JLeather » Mon May 01, 2017 5:48 am

I'm confused by the description/pictures from that link. The description seems to indicate that valve performs all the necessary functions internally including residual pressure, but the diagram in the second picture appears to indicate that you need to plumb in external residual pressure valves?

Txas2step, did you plumb any additional residual pressure valves in your install? I bought a Summit combo valve (760182) which is probably the same as the one in the eBay link (both GM-style valves) but I haven't finished plumbing mine yet.
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Re: Disc brake problem

Postby Txas2step » Mon May 01, 2017 3:26 pm

JLeather wrote:I'm confused by the description/pictures from that link. The description seems to indicate that valve performs all the necessary functions internally including residual pressure, but the diagram in the second picture appears to indicate that you need to plumb in external residual pressure valves?

Txas2step, did you plumb any additional residual pressure valves in your install? I bought a Summit combo valve (760182) which is probably the same as the one in the eBay link (both GM-style valves) but I haven't finished plumbing mine yet.


No additional valves...just make sure you hook it up correctly front/rear. :Thumbsup
61 shorty 170/ 3spd 3:91(sold)
66 lwb 318 poly/727/4:10 (sold)
67 shorty 318poly/4spd 3:55
68 ute 318/3 spd/3:55(sold)
70 318/727/3:23
66 d200 225/4spd/4:10( military)(sold)
68 d100 383/727/3:55
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Re: Disc brake problem

Postby bigblockdodge440 » Tue May 02, 2017 5:55 pm

I have not done the ram charger proportioning valve swap yet. I have to run new brake lines because of different size fittings, don't know when I'll get to it, so if you do yours first let me know how it works.
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Re: Disc brake problem

Postby Conrad » Thu May 04, 2017 8:18 pm

[removed for inaccuracy reasons] Thanks for the info Terry! :Thumbsup
Last edited by Conrad on Fri May 05, 2017 3:37 pm, edited 1 time in total.
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Re: Disc brake problem

Postby PwrWgnDrvr » Thu May 04, 2017 11:06 pm

Actually, the purpose of the rpv is to release the brakes slowly for smooth operation. They function as a one way valve that allows full and quick flow when applying brakes and a slow release. They do not hold pressure in the line for more than a few seconds after release of the pedal, otherwise the shoes would constantly rub on the drums and burn up.
On a side note, some have used a brake master to replace a clutch master. If the rpv is not removed, the clutch does not work properly. (Think instantaneous slave cylinder release to engage the clutch when pedal retracts.)
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Re: Disc brake problem

Postby JLeather » Sun May 07, 2017 6:45 pm

Terry, I've gotta disagree with you on the function of the residual pressure valve. As per Wilwood's website (about 2/3's down the page http://www.wilwood.com/MasterCylinders/ ... alves.aspx):

"Wilwood two pound and ten pound residual pressure valves retain a minimum brake line pressure to help eliminate excessive pedal travel in both disc and drum brake systems."

The residual pressure valves are check valves with a certain psi to overcome the return. They permit free flow to the brakes, and retain the listed pressure between the valve and the brakes. There is some internal leakage (typically measured in drops per minute) so they won't hold the listed pressures indefinitely, but they are designed to try to keep that pressure on the brake side at all times and one in good shape should hold the pressure for several hours. For drums they retain 10 psi which allows the brakes to disengage but doesn't permit the springs in the drums to continue to compress the wheel cylinders. For the most part if your adjusters are working properly and your shoes are arched to the drum ID there won't be a noticeable difference with the RPV installed because the wheel cylinders will be fully compressed at rest anyway, but in a system with small issues they will help reduce excess pedal travel. Since you don't have the same opportunity for issues with a disc system (no arching required, no retract springs, etc) the 2 lb disc valves are really only for systems with an under-floor m/c where gravity will return excess fluid.

To the OP, the proportioning valve should not noticeably impact pedal travel, only the brake bias. You should install a prop valve to keep the rear wheels from getting too much pressure and locking up when wet/empty. For your pedal travel issues, make sure the adjusters in the rear are working properly and if that's all good try a 10 lb RPV in the rear brake line.
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Re: Disc brake problem

Postby PwrWgnDrvr » Mon May 08, 2017 9:13 am

If there is an RPV in the master (standard from the factory), an additional one in the line won't make any difference. Seems foolish to use an RPV as a band-aid for improperly adjusted brakes.

"....if your adjusters are working properly.....there won't be a noticeable difference with the RPV installed because the wheel cylinders will be fully compressed at rest anyway....
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Re: Disc brake problem

Postby JLeather » Mon May 08, 2017 12:36 pm

I don't know when they became standard equipment but the m/c I removed from my '67, as well as the brand new m/c for a '72 that I just installed, did not have internal RPV's. The OP should check his to see if it has an internal one as well. There's a fairly easy test for it. Take a piece of thin wire and gently insert it into the m/c through the brake line port (don't force it). If it goes all the way into the bore of the m/c there is no internal RPV. If it stops before the bore there is an RPV (or you stuck it in crooked... :lol: ). Also if your m/c has solid machined brake line ports there's no RPV internally. The m/c's with internal RPV's will have some sort of pressed-in port because they have to machine the space for the RPV from the outside (at least on the ones I've seen so far).

It is true that you shouldn't use an RPV to cover up for some other brake issue. If your adjusters aren't working, for instance, the RPV will keep the brakes feeling ok but the wheel cylinders will be over extended and could possibly pop a piston out or start leaking suddenly.
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Re: Disc brake problem

Postby PwrWgnDrvr » Mon May 08, 2017 5:11 pm

The master RPV is just a little rubber piece behind the flare surface of the port. Don't push that wire too hard or you will puncture right thru it!
I think its all shown in the FSM. (If not, I saw it somewhere else)
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Re: Disc brake problem

Postby Conrad » Mon May 08, 2017 8:12 pm

All excellent info. :Thumbsup
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